Reactor for the biological treatment of water

ABSTRACT

A reactor for the biological treatment of water comprises a reactor vessel (1), a fermentation chamber (3) bounded in the vessel, inlets (10) for introducing influent into the fermentation chamber, a settling chamber (4) above the top boundary (2) of the fermentation chamber (3), for separating out sludge from treated water, a downer (5) extending downwards from the settling chamber through the fermentation chamber, for returning separated-out sludge to the fermentation chamber (3), and an outlet (11) for discharging effluent from the settling chamber. In order to improve and accelerate the separation of sludge from effluent in a simple manner, at least one supply line (8a, 9a, 17) opens out tangentially into the settling chamber. A whirlpool is produced in the settling chamber by the supply line.

FIELD OF THE INVENTION

The invention relates to a reactor for the biological treatment ofwater, comprising a reactor vessel, a fermentation chamber bounded insaid vessel, means for introducing influent into the fermentationchamber, a settling chamber above the top boundary of the fermentationchamber, for separating out sludge from treated water, a downerextending downwards from the settling chamber through the fermentationchamber, for returning separated-out sludge to the fermentation chamber,and means for discharging effluent from the settling chamber.

BACKGROUND OF THE INVENTION

Such reactors are known for both aerobic and anaerobic treatment ofwater. An example of an embodiment for anaerobic treatment is describedin U.S. Pat. No. 4,609,460.

A driving force for the downward flow of recirculation water and sludgeis obtained by producing a gas lift effect in such a treatment (in whichcase the gas-containing liquid outside the downer is lighter than thenon-gas-containing liquid in the downer).

SUMMARY OF THE INVENTION

The object of the invention is to provide a simple way of improving theseparation of sludge from effluent and also the circulation in thereactor.

According to the invention, for this purpose the reactor ischaracterised in that at least one liquid and/or gas supply line opensout in the settling chamber by way of a tangential discharge end, forproducing a whirlpool in said settling chamber.

SUMMARY OF THE INVENTION

The whirlpool effect arising through the tangential supply of gas intothe settling chamber gives an additional driving force to the downwardflow of separated-out sludge and recirculation water. The sludgeseparation itself is improved.

Where the reactor is intended for anaerobic water purification, thesupply line opening out tangentially into the settling chamber is a pipefor liquid and biogas. In that case it is connected to the fermentationchamber.

Where the reactor is intended for aerobic water purification, the supplyline opening out tangentially into the settling chamber is an air oroxygen pipe.

The gas inlet line opening out into the settling chamber can be situatedwith its outlet end in a space which is separated by a cylindricalpartition from the tangential inlet of the effluent discharge means.

An additional improvement of the downward flow in the downer can also beachieved if the means for introducing influent at least partiallyconsist of one or more pipes opening tangentially downwards into thebottom part of the downer.

In order to prevent short-circuit currents in the bottom section of thereactor and to fluidise the bottom bed on the bottom, a number of gasinlet pipes can open out Just above the bottom of the fermentationchamber. In that case the whirlpool effect and the recirculation canalso be adjusted to some extent with the influent introduction.

In the case of anaerobic purification, the settling in the settlingchamber can be hampered by gas bubbles which occur in the case ofoversaturation of (carbon dioxide) gas in the liquid/sludge mixtureleaving the fermentation chamber. In order to solve this problem, thereactor can be provided with a gas stripper in the form of one or morecascade chambers, into which the liquid/sludge mixture to be supplied tothe settling chamber is introduced, and out of which the liquid/sludgemixture flows through a tangential outlet into the settling chamber.

The cascade chambers are preferably fitted in the annular space betweenthe cylindrical reactor wall and a cylindrical boundary wall of thesettling chamber. A cyclone can be connected upstream of the cascadechambers, in order to separate out the coarse gas.

Of course, the place where effluent is discharged must lie at a gooddistance from the place where the liquid/sludge mixture is suppliedtangentially to the settling chamber. The tangential outlet of thecascade chambers and the inlet of the effluent outlet will therefore lieat an angular distance of little less than 360°, viewed in the whirlpooldirection.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained in greater detail with reference tothe figures, in which examples of a reactor for anaerobic purificationof effluent are shown.

FIG. 1 shows a longitudinal section of the reactor (see I--I in FIG. 2).

FIG. 2 shows a cross-section along the line II--II in FIG. 1.

FIG. 3 shows a cross-section along the line III--III in FIG. 1.

FIG. 4 shows a perspective view of a second embodiment of the whirlpoolreactor according to the invention, in which a part of the cylindricalreactor wall is cut away.

FIG. 5 shows a cross-section near the top edge of the reactor accordingto FIG. 4.

FIG. 6 shows a longitudinal section of the cascade chambers of thedevice according to FIGS. 4 and 5.

DETAILED DESCRIPTION OF THE INVENTION

The reactor shown comprises a relatively high cylindrical reactor vessel1, which is divided by a conical wall 2 into a fermentation chamber 3and a settling chamber 4. A downer 5 extends from the downward-directedtip of the conical wall 2 through the fermentation chamber 3, whichdowner opens out at some distance above the bottom of said chamber.

A cylindrical partition 6 is provided in the settling chamber 4, whichpartition with the outside wall of the vessel I bounds a cylindricalspace 7 into which pipes 8, 9 open out with a tangential discharge end8a, 9a respectively. Each of said pipes 8, 9 is in communication withthe fermentation chamber 3 by way of an opening in the conical wall 2.

Pipes 10 for the supply of water to be treated (influent) open out intothe bottom part of the downer 5, the discharge end 10a of said pipes 10being directed tangentially and slightly downwards relative to thedowner.

A pipe 11 for the discharge of treated water (effluent) extends from aninlet 11a running tangentially inside the space bounded by the partition6 to the exterior of the vessel 1.

The device works as follows:

During the time in which the water to be treated is in the fermentationchamber 3, biogas (in particular methane) is formed. As a result of thecontinuous or batchwise supply of influent through the pipes 10, liquidand biogas will flow through the pipes 8 and 9 into the settling chamber4, where sludge and water are separated, and where biogas separates outfrom the liquid.

A mixture of recirculation water and sludge flows back through thedowner 5 to the bottom of the fermentation chamber 3. Due to the absenceof gas, this mixture is heavier than the gas-containing mixture ofsludge and water present at the outside of the downer 5. The gas lifteffect arising through this weight difference promotes the circulationin the reactor.

Since the pipes 8 and 9 have tangential outflow openings 8a, 9arespectively, a whirlpool is produced in the settling chamber, whichwhirlpool further reinforces and accelerates the separation of sludgeand the circulation of the reactor.

As a result of friction, the flow velocity near the top surface of thewall 2 is lower than it is at a distance above said surface. In additionto the whirlpool flow in horizontal planes (see the top two curvedarrows in FIG. 1), this causes circulation flows in vertical planes (seethe bottom two curved arrows in FIG. 2), which promotes the settlingnear the top end of the downer 5.

The downward flow of sludge and recirculation water in the downer isalso promoted by the tangentially downward running position of theoutflow opening 10a of the influent pipes 10.

The purified water (effluent) passes through the tangential inlet 11ainto the pipe 11 and is discharged through said pipe.

As a result of the infeed of gas (in the case of an anaerobic reactor:biogas) into the sludge bed on the bottom of the reactor through thepipes 12, the sludge bed is fiuidised and short-circuit currents areprevented.

The invention is not restricted to the anaerobic reactor described, butcan also be applied to aerobic reactors. In that case the whirlpooleffect will be produced by air or oxygen which is conveyed through thepipes 8 and 9 into the settling chamber.

The invention leads to an improved and accelerated separation of sludge.

The alternative embodiment according to FIGS. 4, 5 and 6 gives asolution to the problem of small gas bubbles arising throughoversaturation of carbon dioxide in the liquid in the settling chamber,and impeding the settling of sludge. For this purpose, this carbondioxide is for the most part stripped out of the liquid before theliquid is introduced tangentially into the settling chamber.

In the annular space 7, two cascade chambers 13a, 13b are separated bywalls 14 from the remainder of the annular space 7. A cyclone 15 isconnected upstream of said cascade chambers. The overflow wall 16 isplaced between the chambers 13a and 13b. A pipe 17 extends tangentiallyfrom the inward facing side wall of the cascade chamber 13b, for thetangential supply of liquid into the settling chamber 4, which liquidhas the carbon dioxide stripped from it. An opening 18 in the insidewall of the annular space 7 admits effluent from the settling chamber 2into a chamber 19 below the bottom 20 of the first cascade chamber 13a.An effluent discharge pipe 24 (comparable to the pipe 11 in FIGS. 1 and2) extends downwards from the bottom of the chamber 19. The top end 21of the cyclone 14 is the discharge outlet for coarse gas above theliquid in the annular space 7. The liquid discharge outlet 22 at thebottom end of the cyclone is connected to a pipe 23 which extendsupwards in the first cascade chamber 13a, and the outlet of whichprojects beyond the surface of the liquid in said chamber 13a, so that acascade of liquid can flow into the cascade chamber 13a.

The mixture of liquid, sludge and gas which has passed into the annularspace flows through the inlet 15a into the cyclone 15, where the coarsegas is separated from the liquid and leaves the cyclone at the top end21. The liquid/sludge mixture with oversaturated carbon dioxidedissolved therein leaves the cyclone at 22 and flows through the top endof the pipe 23 into the first cascade chamber 13a, and then over the topedge of the wall 16 into the second cascade chamber 13b. Theoversaturated carbon dioxide is released as a result of the cascadeformation and passes into the air above the surface of the liquid in theannular space 7, where together with the carbon dioxide separated out bythe cyclone it is extracted through a gas discharge pipe 25.

The liquid which has reached the settler 2 through the tangential pipe17 has most of the dissolved carbon dioxide removed from it and will beconveyed in a whirlpool flow, in the manner described with reference tothe embodiment according to FIGS. 1 and 2, without carbon dioxidebubbles having an impeding effect. Sludge settlement near the inlet ofthe downer 5 is promoted and the liquid which is high in sludge and lowin gas flows through the downer to the underside of the fermentationchamber 3.

A cover (not shown) is placed on the reactor vessel.

Due to the fact that the opening 18--viewed in the direction of rotationof the whirlpool--is a little less than 360° away from the tangentialoutlet 17, the sludge has sufficient opportunity to settle before theeffluent is discharged through opening 18, chamber 19 and pipe 24.

I claim:
 1. Reactor for the biological treatment of water comprising areactor vessel, a fermentation chamber bounded in said vessel, means forintroducing influent into the fermentation chamber, a settling chamberdisposed above a top boundary of the fermentation chamber, forseparating out sludge from treated water, said settling chamber havingan outer boundary formed as a body of revolution, at least one supplyline having a discharge end opening into the settling chamber, a downerextending downwards from the settling chamber through the fermentationchamber for returning separated sludge to the fermentation chamber, andmeans for discharging effluent from the settling chamber, said dischargeend of the supply line having a tangential direction, perpendicular tothe radius as seen in a plane perpendicular to the axis of the settlingchamber, for producing a whirlpool in said settling chamber, saidwhirlpool creating an additional driving force to the downward flow ofseparated sludge through the downer.
 2. Reactor according to claim 1,intended for anaerobic water purification, wherein the supply lineopening out tangentially into the settling chamber is a pipe for liquidand biogas.
 3. Reactor according to claim 2, wherein the supply line isin communication with the fermentation chamber.
 4. Reactor according toclaim 1, intended for aerobic water purification, wherein the supplyline opening out tangentially into the settling chamber is a pipe forliquid, and air or oxygen.
 5. Reactor according to claim 1, wherein themeans for discharging effluent from the settling chamber has atangential inlet mouth positioned near the liquid level in the settlingchamber.
 6. Reactor according to claim 5, wherein the supply lineopening out into the settling chamber is a pipe situated with itstangential outlet end in a space which is separated by a cylindricalpartition from the tangential inlet mouth of the effluent dischargemeans.
 7. Reactor according to claim 1, wherein the means forintroducing effluent comprises at least one pipe opening out into alower part of the downer and having a tangentially downwardly orientedoutlet end.
 8. Reactor according to claim 1, further comprising a numberof gas inlet pipes disposed just above the bottom of the fermentationchamber.
 9. Reactor according to claim 1, for anaerobic waterpurification, wherein the reactor is provided with a gas strippercomprising cascade chambers into which liquid/sludge mixture to besupplied to the settling chamber is introduced, and out of which theliquid/sludge mixture flows through a tangential outlet into thesettling chamber.
 10. Reactor according to claim 9, wherein the cascadechambers are provided in an annular space between a cylindrical wall ofthe reactor vessel and a cylindrical wall of the settling chamber. 11.Reactor according to claim 10, wherein the inside wall of the annularspace comprises an opening for admitting effluent from the settlingchamber into a chamber below the bottom of the first cascade chamber,said chamber being in communication with an effluent outlet, and saidtangential outlet of the cascade chambers at said opening lying at anangular distance of little less than 360°, viewed in the whirlpooldirection.
 12. Reactor according to claim 9, further comprising acyclone connected upstream of the cascade chambers, for separatingcoarse gas from the sludge/liquid mixture.